In general, in a developing unit of an electrophotography image forming apparatus or the like such as a copier or a printer, as shown in FIG. 3, an image forming body 11 such as a photoconductor retaining an electrostatic latent image, a developing roller 12 which makes the electrostatic latent image a visible image by making the image forming body 11 come in contact with the roller and attaching toner 20 which is supported on the surface of the roller to the image forming body 11, and a toner-conveying roller 13 (including a toner-providing roller and a cleaning roller for sweeping off unwanted toner) for providing the developing roller 12 with toner are provided, and an image formation is performed by a series of processes in which the toner 20 is conveyed from a toner storage unit 14, via the toner-conveying roller 13 and the developing roller 12, to the image forming body 11. In this figure, 15 represents a transfer roller, 16 a charge unit, 17 an exposure unit, and 18 a blade for sweeping off toner.
Among these, the toner-conveying roller 13 is formed in a structure that an electrically conductive elastic body such as polyurethane foam is supported on the periphery of the axis via an adhesion layer from a viewpoint that the toner-conveying roller 13 should not damage the developing roller 12 by coming in contact with the developing roller 12, and from a viewpoint that a grip performance is ensured by increasing contact area of the rollers or the like. Examples of functions required for the toner-conveying roller 13 include a toner conveying ability, a toner charging ability, and a toner sweeping ability. In order to satisfy these functions, various measures have been taken.
For example, by using a method in which electrically conductive treatment liquid such as electrically conductive carbon black or the like is impregnated in a polyurethane foam which constitutes the toner-conveying roller 13 (see, Patent Documents 1 to 3), or by using a method in which an electrically conductive carbon is kneaded, an electric resistance is reduced, a toner charge amount (Q/M) is decreased, and a toner conveying amount (M/A) is heightened, whereby a failure of an image blur during an endurance image evaluation has not been allowed to occur.
Without using an electrically conductive material such as carbon, by embossing the surface of the toner-conveying roller 13 to heighten physically the toner conveying amount (M/A), a failure such as an image blur during an endurance image evaluation has not been allowed to occur (see, Patent Document 4).
Further, it has been known that the toner conveying ability increases by exposing apart of fine particles for charging toner from an elastomeric foam layer (see Patent Document 5).